The prior art discloses a number of new ways to increase the sensitivity of photographic silver halide emulsions. Urbach, U.S. Pat. No. 2,449,153, discloses an emulsion containing cysteine. Scavron, U.S. Pat. No. 3,505,025, discloses the use of thiazolidines in photographic films. Plakunov and Koller, U.S. Pat. No. 3,708,302, discloses that the reaction product of cysteine and glutaraldehyde can be employed in a layer on the same side of the support as a silver halide emulsion layer. Elsner, et al U.S Pat. No. 4,243,748. describes the combination of a thiazolidine-compound and a disulfide. Thus, over the years it has come to be recognized that the sensitivity of silver halide films could be increased by incorporating a cysteine or thiazolidine moiety in one or more layers. However, there is a problem of metal contamination.
It is generally known that chelating agents may be added to a photographic element to control or eliminate defects caused by metal contamination. A chelating agent forms a stable complex with undesirable metal ions to prevent them from interfering with the silver imaging process. Sidwell, U.S. Pat. No. 4,340,665, describes a synergistic combination of chelate and phosphate for counteracting iron contamination in silver halide films. Earlier references have described various amine and quinoline chelating agents for use in photographic emulsions and photographic developers to avoid problems with iron contamination.
Quinoline compounds are also known to be useful in photographic films for purposes other than chelates for undesirable metal ions. Jones et al. U.S. Pat. No. 2,578,655, discloses improved image color with 4-hydroxyquinolines. Dersch et al. U.S. Pat. No. 3,446,618, describes the use of a 4-hydroxyquinoline carboxylic acid salt as a stabilizer.
It has now been discovered that severe development artifacts which occur in photographic films containing AgIBr emulsions sensitized with cysteine and/or thiazolidine moieties due to nonferrous contamination, viz., Al, Cu, or Zn, can be substantially reduced or eliminated by the incorporation of chelating agents in one or more layers of the film.